Process For the Rectification of Mixtures of High-Boiling Air-and/or Temperature-Sensitive Useful Products

ABSTRACT

According to the invention, a process for the rectification of mixtures of high-boiling air- and/or temperature-sensitive substances which require a high separation efficiency is proposed, in particular a process for the working-up of a VE- or VEA-containing product stream. The process is characterized in particular in that, in a first purification stage, low-boiling products and unspecified isomers of the useful product are separated from the product stream virtually without loss of useful product and that, in a second purification stage, the useful product is removed in a stream having a purity of &gt;97% by weight and a further stream having a purity of &gt;92% by weight. A preferred embodiment of the process serves for working up VEA, in which the loss of useful product in the first purification stage is less than 5%, based on that amount of VEA in the feed which is added to the purification stage per unit time. Furthermore, the first purification stage may comprise a rectification column ( 1 ), from the top (Ia) of which the low-boiling products and the unspecified isomers of VEA are taken off, a stream containing the useful product in purified form being taken off at the side ( 15 ) and/or at the bottom (Ib) of the column ( 1 ).

The invention relates to a process for the rectification of mixtures ofhigh-boiling air- and/or temperature-sensitive substances, in particularthe rectification of tocopherol acetate—also referred to as vitamin Eacetate (VEA)—for separating lower-boiling and higher-boiling impuritiesfrom the useful product.

The VEA obtained by esterification of vitamin E with acetic anhydride,also referred to below as crude VEA, can be freed from the substantialresidues of acetic acid and acetic anhydride and other impurities, forexample, by multistage distillation steps in falling-film evaporators,thin-film evaporators, etc. Usually, such a reaction mixture thencontains about 94% by weight of VEA, 1-2% by weight of low-boilingsubstances (chiefly phytadienes), about 2-3% by weight of unspecifiedisomers of the useful product (VEA) and 1-2% by weight of high-boilingsecondary components.

In the industrial purification of a VEA-containing product stream, forexample, cascades of short-path evaporators are used. As complete aspossible a separation of the low-boiling substances from the productstream flowing to the cascade of short-path evaporators is decisive forthe dimensioning and the operation of the short-path evaporators and thevacuum system at the required, very low pressures. A thin-filmevaporator usually operated at about 1 mbar and intended for removingthe low boilers is therefore connected upstream of the cascade ofshort-path evaporators. The vapour stream produced in the thin-filmevaporator contains substantially phytadienes, vitamin E acetate andresidues of acetic acid and acetic anhydride and is virtually completelycondensed in a downstream condenser system. Owing to the high content oflow boilers, the condensate obtained cannot be further used and isdiscarded. Because of the position of the phase equilibrium, theproportion of VEA in this vapour stream is about 13% by weight and theloss of VEA is about 2.7%, based on the inflowing amount of VEA. A lowboiler fraction of, usually, about 2% by weight remains in the usefulproduct (bottom product of the thin-film evaporator). The bottom productof the thin-film evaporator is fed to the cascade of short-pathevaporators, in which the VEA is further enriched by repeatedevaporation and condensation.

The process described above and intended for obtaining VEA has thefollowing disadvantages. As already mentioned, a part of the usefulproduct (VEA) passes out of the thin-film evaporator via the gas phaseto the downstream condenser system and is finally lost. Furthermore,only parts of the low boilers are separated off in the thin-filmevaporator, which is per se a relatively complicated and expensiveapparatus, and the rest remains in the useful product and has to beseparated off later on by a complicated procedure. At the same time,owing to the incomplete separation of the main product from thebyproducts in the respective purification steps, this process alsoincludes recycled streams which have to be fed back to the process by arelatively complicated procedure.

Since VEA is being used to an increasing extent for human nutrition orprophylaxis in healthcare, the purity of this product has to meetincreasingly high requirements. The VEA quality required for theseintended uses, also referred to below as “pharma grade” (PG) quality, isdefined as follows:

-   -   Purity >97.5% by weight    -   Colourless to slightly greenish yellow

VEA obtained from the process described above has a purity of <97% byweight. With a purity of >92% by weight, it fulfils the condition whichis set for the so-called “technical grade” (TG) quality of the usefulproduct but not the requirements of a PG quality. For use as a foodadditive or for medical applications, it must therefore be subjected tofurther purification steps.

It is known that, in the working up of product mixtures by distillation,the best results are generally obtained when so-called countercurrentdistillation (also referred to as rectification) is used, i.e. a specialdistillation process with countercurrent flow of descending reflux andascending vapour in rectification columns. It is usual to use columns inwhich the mixture to be separated is introduced in the middle part ofthe column, the vapour becomes enriched with more readily volatilecomponents on its way through the column from bottom to top and thereflux becomes enriched with more sparingly volatile components from topto bottom. The transport of material and heat is intensified by elementsinstalled in the column, such as column trays, random packings orstructured packings, which ensure a sufficient contact time of thephases and a sufficiently large phase boundary.

It is furthermore known that, for the separation of high-boiling,temperature-sensitive mixtures of substances which require a highseparation efficiency, which also includes the mixture present here(crude VEA), it is preferable to use rectification columns which havepackings composed systematically in a regular geometry and havingdefined passage regions for countercurrent phases. This is the case inparticular because, compared with random packings, regularly structuredpackings are distinguished by a higher load capacity and a betterseparation effect, have a smaller specific pressure drop and require asmaller volume of packings and therefore also permit a smaller mass andheat transfer height. Structured packings are therefore used in allvacuum rectifications, in which, owing to the temperature sensitivity ofthe mixture to be separated, a limitation of the column pressure drop isparticularly important. Column packings known for this intended use aremetal fabric packings of the BX and CY type from Sulzer, expanded metalpackings of the Optiflow or Mellapak type and Rhombopak type from Sulzerand Kuhni, respectively, and similarly effective metal fabric packingsfrom other companies, such as Montz GmbH.

The rectification of a VEA-containing mixture is disclosed, for example,in WO 97/02880. However, the rectification generally advantageous forthe purification of products on an industrial scale presents majorproblems in this case owing to the high boiling point of VEA and itsdecomposability at higher temperatures. Substantially distillation underhigh vacuum or even molecular distillations are therefore carried out inorder to be able to distil VEA at as low temperatures as possible.

In spite of the use of the high vacuum, in general only purities of97.3% (DE-A 27 43 920), 98% (DE-A 42 08 477 and JP-B-58 011 869), 98.5%(U.S. Pat. No. 3,459,773) or 98.5 to 99% (DE-A 21 60 103) are achievedaccording to the prior art. Purities above 99% were achieved only bymolecular distillation, namely purities of 99.3% according to JP-A51/14671 and 99.5% according to JP-A-62/226976, it being necessary topoint out that, on investigation by the more precise methods of analysisused today and with the use of purer comparative substances, presumablylower purity values would be achieved. In addition, the distillationyields achievable in this manner are in each case very low, and both thecapital costs and the ongoing operating costs of such plants aretherefore very high owing to the extreme complexity.

It is the object of the invention to provide a process for therectification of mixtures of high-boiling air- and/ortemperature-sensitive useful products, but in particular a process forworking up a VEA-containing product stream, which process does not havethe above-mentioned disadvantages and which permits an economicalmethod, which is simple in terms of process engineering, for separatingoff the useful product in high purity and high yield. In addition, theprocess should also permit the use of separation apparatuses which aresimple in terms of process engineering and should make it possible toprepare two end products in different and optionally variableproportions, which end products differ in their purity. It is alsoconsidered advantageous to develop a process without recycling fortreatment of the products under milder conditions.

This object is achieved by a process having the features of Patent claim1.

Advantageous embodiments of the invention form the subject of thedependent Claims.

Claim 1 proposes a process for the rectification of mixtures ofhigh-boiling air- and/or temperature-sensitive substances which requirehigh separation efficiency, in particular a process for working up a VE-or VEA-containing product stream, which is characterized in that, in afirst purification stage, low-boiling products are separated from theproduct stream virtually without loss of useful product, and unspecifiedisomers of the useful product are taken off, and that, in a secondpurification stage, the useful product is removed in one stream with apurity of >97% by weight and in a further stream with a purity of >92%by weight.

According to the invention, a completely novel concept for thepurification of high-boiling air- and/or temperature-sensitivesubstances, for example VEA, was developed. Only pure waste streams (lowboilers, i.e. streams of low-boiling substances/streams comprisingunspecified isomers of the useful product/streams of high-boilingbyproducts, in each case having a very low VEA content) and pure productstreams form. Thus, no streams which require further working-up areproduced, which also permits the elimination of disadvantageousrecycling.

A preferred embodiment of the process serves for working up VEA, inwhich the loss of the useful product in the first purification stage isless than 5%, based on the amount of VEA in the feed which is added tothe purification stage per unit time. In this particular case, the firstpurification stage may comprise a rectification column, from the top ofwhich the low-boiling products and the unspecified isomers of VEA aretaken off, a stream containing the useful product in purified form beingtaken off at the side and/or at the bottom of the column.

The side take-off or the bottom take-off of the first rectificationcolumn can then be fed, in the second purification stage, to a secondrectification column, from which VEA is then removed either

-   -   as a bottom take-off having a purity of >97% by weight and as a        top take-off having a purity of >92% by weight, or    -   as a side take-off having a purity of >97% by weight and as a        mixture consisting of top take-off and distillate of the bottom        take-off having a purity of >92% by weight.

According to the invention, the two rectification columns havestructured packings having a ratio of separation efficiency to pressuredrop of, preferably, >15 theoretical plates per mbar of pressure drop(basis: F factor=1 Pa^(0.5), column diameter 1 metre, test mixturecis-/trans-decalin). A particularly suitable structured packing is theOPTIFLOW packing from Sulzer AG. According to the invention, at leastthe side take-off is effected at the second column by partialcondensation in a manner such that the product to be separated offleaves the column as condensate and not as a product stream in vapourform. For this purpose, the columns incorporate, important designdetails which are important for the condensation process.

The advantages of the preferred processes according to the invention arethe following:

-   -   A sharp separation in one column is achieved. Usually, a        plurality of columns is required for this purpose.    -   In particular the first column has a high separation efficiency        in combination with a small pressure drop.    -   The losses of products are very small.    -   The purity of the pharma grade product is very high, with a VEA        content of ≧97% by weight.    -   The process is very flexible with regard to the amounts of        product to be produced in PG or TG quality.

In a further preferred embodiment of the invention, before crude VEA isfed to the first column, the product stream is passed for degassing intoa falling-film evaporator in which in particular the low-boilingsubstances, such as, for example, solvent residues, and any remainingtraces of acetic acid and acetic anhydride are removed. The falling-filmevaporator can also be designed thereby in such a way that it alsoserves for reducing the total chlorine content in the crude VEA, inorder thereby to avoid any disadvantageous corrosion in the followingstages. In the first column, the remaining low-boiling substances andthe unspecified isomers of the useful product are then separated off atthe top, and the VEA is removed as a side take-off in vapour form with acontent of >96%. For the preparation of the “pharma grade” quality, theside take-off stream of the first column is rectified again in thesecond column. According to the invention, the “pharma grade” quality istaken off as a side take-off. The bottom product from the first columnis squeezed out in a short-path evaporator and gives the VEA-TG as adistillate together with the top product of the second column.

The invention is explained in more detail below with reference to thedrawing.

In the drawing,

FIG. 1 shows a schematic diagram of the process according to theinvention, designed for working up VEA,

FIG. 2 shows an alternative method of carrying out the process accordingto FIG. 1 and

FIG. 3 shows a side take-off point as provided according to theinvention in the second and, if required, first rectification column.

The procedure shown in FIG. 1 for the preparation of VEA has thefollowing organization. The crude VEA originating from the acetylationstage 5 (conversion of vitamin E into VEA, including separating off themain portion of acetic acid and acetic anhydride) is fed to the degasser3 (falling-film evaporator). There, the remaining low-boilingcomponents, such as, for example, acetic acid or acetic anhydride, areremoved via the line 2. The degassed crude VEA obtained at the bottom ofthe degasser 3 is added as feed approximately in the middle of therectification column 1. At the top la of the column 1, lower-boilingcomponents and unspecified isomers of the useful product are removed viathe line 9 virtually without loss of useful product. The bottom take-offobtained at the bottom 1 b of the column 1 is fed via the line 11 to theshort-path evaporator 13. The loss of the useful product VEA via the toptake-off of the first rectification column 1 is <5%, preferably <1% andideally <0.5%, based on that amount of VEA in the feed which is added tothe column per unit time.

The column 1 furthermore-has a side take-off 15 which is present belowthe column feed. The side take-off of the column 1 is connected via theline 17 to a second rectification column 19, here too the feed beingarranged approximately in the middle of the column. The bottom take-offformed at the bottom 19 b of the column 19 is fed to the short-pathevaporator 13 via the line 23 together with the bottom take-off of thecolumn 1 via the line 11. In the short-path distillation, a residuestream 4 and a distillate stream 25 are obtained. The distillate stream25 is mixed with the top take-off obtained at the top 19 a of the column19.

According to the invention, the column 19 also has a side take-off 27,as described in more detail below. Furthermore, both columns 1 and 19each have a condenser arranged in the top 1 a and 19 a, respectively,and an evaporator provided in the bottom 1 b and 19 b, respectively.These components which as such are conventional and customary forrectification columns are generally known to a person skilled in the artand are therefore neither described in detail nor shown in the drawing.According to the invention, the two rectification columns are packedwith structured packings, the ratio of separation efficiency to pressuredrop of which is greater than 15 theoretical plates per mbar pressuredrop (basis: F factor 1 Pa^(0.5), column diameter 1 metre, test mixturecis-/trans-decalin). The principle of the process according to FIG. 1 isdistinguished by the fact that the remaining traces of low-boilingcomponents, such as, for example, acetic acid, acetic anhydride orsolvent residues from the product stream arriving from the acetylation,are removed from the crude VEA in the upstream degasser 3 and aretransported away via the line 2.

In the first column 1, the remaining lower-boiling components and alsothe unspecified isomers of the useful product are then separated off atthe top 1 a, and a VEA having a content of >96% by weight is removed atthe side take-off point 15 by partial condensation.

According to the invention, the column 1 is operated as follows:

-   -   The side take-off comprises about 75% by weight, based on the        feed stream added, this having as high a VEA content as possible        with a small amount of unspecified isomers of the useful product        and high-boiling components.    -   The top take-off comprises about 2 to 5% by weight, based on the        feed stream.    -   The top condenser arranged in the top 105a virtually completely        condenses the incoming vapour stream to give reflux and top        take-off.    -   The pressure at the top of the column is preferably about 0.5 to        1 mbar and is as far as possible kept constant, and the column        temperatures are between 190 and 280° C., depending on the        loading of the column.

On maintaining these guide parameters, and depending on the establishedreflux ratio of column 1, the latter can be operated so that the VEAcontent in the side take-off is well above 95% by weight and that in thetop take-off is substantially below 20% by weight.

The side take-off of the first column 1 is fed via the line 17 to thesecond column 19 in order to prepare VEA-PG. The take-off of thisquality is in turn effected as a side take-off by partial condensationat position 27 and is removed from the plant via product line 29.

The bottom product emerging from the bottom 1 b of the first column 1 issqueezed out together with the bottom product of the second column 19 inthe short-path evaporator 13 and gives a distillate which, together withthe product of the second column 19, emerging from the top 19 a of thesecond column 19, forms the VEA-TG.

In the alternative method of carrying out the process for thepreparation or purification of the VEA products, shown in FIG. 2, thereis no side take-off from the first column 1. Instead, the bottom productof the column 1 is transported via the product stream line 11 directlyand completely to the second column 19. As a result of this, the feed tothe short-path evaporator consists only of the bottom take-off of thecolumn 19, and in this case the VEA-TG is formed only from the mixtureof the top product and the distillate of the bottom product of thesecond column 19.

The side take-off by partial condensation in the columns 19 and/or 1 isdecisive for carrying out the preferred process according to theinvention. This side take-off will therefore be explained in more detailbefore the purification of VEA is described in more detail withreference to two specific examples.

In the section of the two rectification columns 1 and 19 according tothe invention, shown in FIG. 3, the countercurrent flow is characterizedby the descending reflux-stream 31 and ascending vapour stream 33 in therectification column, in the region of the side take-off point thevapour flowing through the packings and separating elements of the sidetake-off from bottom to top, and the reflux flowing inside a guide pipefrom top to bottom.

A distributor 35 which redistributes the reflux from the collector bed37 above the side take-off is present in the lower region of the sidetake-off point. In order to avoid contamination of the (vapour) sidetake-off with liquid, a half layer of Mellapak 250X is installed as asplash guard 39. Directly above this layer 39, the collector 41 for theside take-off is provided. The collector 41 empties, for example, into atrap 43 which opens into an outlet 45 intended for removal of the vapourcondensate to be separated off. Above the collector 41 there follows aside take-off partial condenser 47 which, for example, is in the form ofa U-tube bundle heat exchanger and serves for producing the vapourcondensate. A total take-off collector 37, which transports thereflux—as already mentioned—from the upper part of the side take-offpoint past the partial condenser 47 into the lower distributor 35 ispreferably present as the uppermost element. It is advantageous that thecollector 37 carries out a total take-off so that the side take-off isnot contaminated by the reflux or adversely affects the colour of theside take-off.

According to the invention, the side take-off is effected by partialcondensation of the vapour phase ascending in the column. This has theadvantage that a vapour condensate, i.e. not a product stream in vapourform, is taken off as a side take-off, with the result that the pressuredrop caused by the take-off and owing to the smaller volume streams ofthe liquids can be significantly reduced. Since the take-off involves apartial condensation, an additional purification stage is furthermoreobtained, which also proves to be particularly advantageous.

It should be pointed out here that the process described with referenceto FIGS. 1 and 2 represents only one working example of the inventionand that in particular the design of the plant which serves for carryingout the process can vary in different respects within the scope ofprotection defined by claim 1. Thus, the process according to theinvention and the partial side take-off can also be used for thepurification of vitamin E (VE) and of course also for the working-up orpurification of other substances which, like VE and VEA, arehigh-boiling and temperature-sensitive and are usually purified by meansof rectification columns.

The processes described above with reference to FIGS. 1 and 2 will nowbe described in detail by means of two specific examples.

EXAMPLE 1 With Reference to FIG. 1

Synthetically prepared crude VEA having a content of about 90 to 92% ofVEA, about 2-3% of low-boiling components (chiefly phytadienes), about2-3% of unspecified isomers of the useful product (VEA) and about 3-4%of high-boiling components is degassed in a falling-film evaporator at185° C. and about 3 mbar. The degassed crude VEA is fed in at atemperature of between 180 and 250° C. approximately in the middle ofthe rectification column 1 with a packing height of 6 to 8 m of theSulzer Optiflow C36 type. The pressure at the top of the column is about0.5 to 1 mbar. At the top of the column 1, about 4% by mass of thefeed-stream is removed as a top take-off with a content of about 3% ofVEA. The column 1 is operated at a reflux ratio of about 10 to 20. Theside take-off point is about 2 to 3 m of packing height below the feedinflow point. About 75% of the feed stream having a VEA content of about96-97% are removed at the side take-off. The desired flow rate is set byregulation of the partial condenser forward flow temperature. Theproduct obtained at the bottom of the column 1 at a temperature of 260to 270° C. still contains about 80-82% of VEA.

The side take-off of the column 1 having a VEA content of about 96 to97% is then added at a temperature between 180 and 250° C. as feedapproximately in the middle of the rectification column 19 having apacking height of 6 to 8 m of the Sulzer Optiflow C36 type. The pressureat the top of the column 19 is about 0.5 to 1 mbar. At the top of thecolumn 19, about 5 to 15% by mass of the feed stream are removed as atop take-off having a content of about 92 to 95% of VEA. The column 19is operated at a reflux ratio of about 15 to 30. The side take-off pointis about 2 to 3 m of packing height below the feed inflow point. At theside take-off, depending on the desired amount of PG, between 50 and 78%(the latter corresponds to 60% of the VEA used in the form of PG) of thefeed stream with a VEA content of more than 97% are removed. The desiredflow rate is established by regulation of the partial condenser forwardflow temperature. The product obtained at the bottom of the column 19 ata temperature of 260 to 270° C. still contains about 90-95% of VEA,depending on the split ratio set.

The bottom products of the columns 1 and 19 are now fed to theshort-path evaporator 13, which is operated at a pressure of about 0.1to 0.2 mbar. The residue still contains about 2-5% of VEA, while the VEAcontent in the distillate is about 92%. The distillate is mixed togetherwith the top take-off of the column 19 to give VEA TG.

EXAMPLE 2 With Reference to FIG. 2

Synthetically prepared crude VEA having a content of about 90 to 92% ofVEA, about 2-3% of low-boiling components (chiefly phytadienes), about2-3% of unspecified isomers of the useful product (VEA) and about 3-4%of high-boiling components is degassed in a falling-film evaporator at185° C. and about 3 mbar. The degassed crude VEA is fed in at atemperature of between 180 and 250° C. approximately in the middle ofthe rectification column 1 with a packing height of 6 to 8 m of theSulzer Optiflow C36 type. The pressure at the top of the column is about0.5 to 1 mbar. At the top of the column 1, about 4% by mass of the feedstream is removed as a top take-off with a content of about 3% of VEA.The column 1 is operated at a reflux ratio of about 10 to 20. Theproduct obtained at the bottom of the column 1 at a temperature of 260to 270° C. contains about 93-95% of VEA.

The bottom take-off of the column 1 having a VEA content of about 93 to95% is then added at a temperature between 180 and 250° C. as feedapproximately in the middle of the rectification column 19 having apacking height of 6 to 8 m of the Sulzer Optiflow C36 type. The pressureat the top of the column 19 is about 0.5 to 1 mbar. At the top of thecolumn 19, about 5 to 15% by mass of the feed stream are removed as atop take-off having a content of about 92 to 95% of VEA. The column 19is operated at a reflux ratio of about 15 to 30. The side take-off pointis about 2 to 3 m of packing height below the feed inflow point. At theside take-off, depending on the desired amount of PG, between 40 and 60%(the latter corresponds to 60% of the VEA used in the form of PG) of thefeed stream with a VEA content of more than 97% are removed. The desiredflow rate is established by regulation of the partial condenser forwardflow temperature. The product obtained at the bottom of the column 19 ata temperature of 260 to 270° C. still contains about 82-87% of VEA,depending on the split ratio set.

The bottom product of the columns 19 is now fed to the short-pathevaporator 13, which is operated at a pressure of about 0.1 to 0.2 mbar.The residue still contains about 2-5% of VEA, while the VEA content inthe distillate is about 92 to 95%, depending on the split. Thedistillate is mixed together with the top take-off of the column 19 togive VEA TG.

1. Process for the working-up of high-boiling air- and/ortemperature-sensitive substances, in particular vitamin E acetate,characterized in that, in a first purification stage, low-boilingproducts and unspecified isomers of vitamin E acetate are taken off fromthe product stream virtually without loss of useful substance and that,in a second purification stage, the useful product is removed in onestream with a purity of >97% by weight and a further stream with apurity of >92% by weight.
 2. Process according to claim 1, characterizedin that the loss of useful product in the first purification stage isless than 5%, based on that amount of VEA in the feed which is added tothe purification stage per unit time.
 3. Process according to claim 1,characterized in that, in the first purification stage, the productstream is fed to a rectification column (1), the low-boiling productsand the unspecified isomers of the useful product being taken off at thetop (Ia) of this column, and a stream containing the useful product inpurified form being taken off at the side (15) and/or at the bottom (Ib)of the column (1).
 4. Process according to claim 3, characterized inthat the side take-off or the bottom take-off of the first rectificationcolumn is fed in the second purification stage to a second rectificationcolumn, and that the useful product is removed from the second column asa bottom take-off with a purity of >97% by weight and as a top take-offwith a purity of >92% by weight.
 5. Process according to claim 3,characterized in that the side take-off or the bottom take-off of thefirst rectification column (1) is fed in the second purification stageto a second rectification column (19), and that the useful product isremoved from the second column (19) as a side take-off with a purityof >97% by weight and as a mixture consisting of top take-off anddistillate of the bottom take-off with a purity of >92% by weight. 6.Process according to claim 4, characterized in that the bottom take-offof the second column is distilled before it is mixed with the toptake-off of the same column.
 7. Process according to claim 4,characterized in that the product stream is degassed in a falling-filmevaporator (3) before it is added to the first column (1).
 8. Processaccording to claim 4, the side take-off of the first column (1) beingpassed into the second column (19), characterized in that the bottomtake-offs of both columns (1, 19) are mixed with one another and aredistilled and, together with the top take-off of the second column, formthe useful product having a purity of >92% by weight.
 9. Processaccording to claim 4, characterized in that the distillation is effectedin a short-path evaporator (13).
 10. Process, in particular according toclaim 4, characterized in that the side take-off is effected by partialcondensation of the vapour phase ascending in the column (1, 19) and thelaterally emerging product stream is removed as vapour condensate fromthe column.
 11. Process according to claim 10, characterized in that thevapour condensate has a purity of >97% by weight.
 12. Rectificationcolumn (1, 19) for carrying out a side take-off according to claim 10 or11, comprising a descending reflux stream (31) and ascending vapourstream (33) in the rectification column (1, 19) and packings installedin the column (1, 19) for intensifying the mass and heat transport,characterized by a side take-off section comprising: a product streamdistributor (35) which redistributes the reflux from the collector bed(37) above the side take-off, a splash guard (39) above the productstream distributor (35), a product stream collector (41) which isintended for the side take-off and opens into a lateral vapourcondensate outlet (45), a side take-off partial condenser (47) arrangedabove the collector (41) and a collector (37), preferably a totaltake-off collector above the side take-off partial condenser (47).